The present invention relates to a hybrid electric vehicle and more particularly to a park pawl integrated with a transmission for such a vehicle.
Series type hybrid electric vehicles have an electric generator driven by a thermal engine to supply electrical power to the vehicles"" battery and electrical power distribution system, which in turn support operation of an electric drive motor. Unlike parallel type electric vehicles which have a drive line which may be driven directly by the thermal engine, series type electric vehicles are driven by only the electric drive motor. The term series refers to the path of energy from the thermal engines to the drive line and hence to a powered axle and wheels. Several advantages follow from this arrangement. For example, if the drive motor does not require power and the thermal engine is running, then all electrical power can be used to charge the battery, and run other electrical power using systems. Further, the drive motor and thermal engine may be positioned on the vehicle chassis substantially without consideration of one another.
The drive motor is connected to the driven axle through a gear reduction or transmission type device and a drive train. The transmission is based on a ring or planetary gear set comprising several rotatable elements. Park brakes have been provided in such vehicles through a mechanical, non-fluid operated mechanism in proximity to the drive train, such as illustrated in U.S. Pat. No. 6,186,253. However, park pawls as commonly found in automatic transmissions, which provide a back up to park brakes, have not readily duplicated with off the shelf motors and gear reduction devices used for transmissions in hybrid vehicles. Nor is the possibility of leaving the vehicle in gear to use the thermal engine as a brake available. What is needed is a mechanically reliable and easily implemented park pawl for electric vehicles.
According to the invention there is provided a transmission for an electric motor. The transmission comprises a housing, rotatable elements located within the housing and coupled to be driven by a drive motor, a locking plate located within the housing and coupled thereto for movement into and out of engagement with a first of the rotatable elements to prevent rotation of the rotatable elements, a plurality of slots around an outer perimeter of one face of the first rotatable element, a plurality of cooperating teeth disposed on one face of the locking plate for engaging the plurality of slots on the first rotatable element, means for preventing rotation of the locking plate, and means for urging the locking plate linearly into and out of engagement with the first rotatable element. An electromagnet is affixed to the housing behind the locking plate relative to the first rotatable element for drawing the locking plate away from the first rotatable element when energized. A spring is positioned with respect to the locking plate and electromagnet for urging the locking plate into engagement with the first rotatable element. A plurality of guide pins is affixed to the back of the locking plate, the guide pins being positioned to move into and out of openings in the electromagnet to define a linear travel for the locking plate to and from the first rotatable element while preventing rotation of the locking plate with the first rotatable element. A spring actuated catch for each guide pin is located with respect to the electromagnet for engaging its respective guide pin when the locking plate reaches a travel limit in the direction away from the first rotatable element. A solenoid is associated with each spring actuated catch for releasing the spring actuated catch from its respective guide pin.
Additional effects, features and advantages will be apparent in the written description that follows.